1. Field
The present disclosure relates generally to liquid-cooled light-emitting diode (LED) bulbs and, more specifically, to providing an expandable volume in an LED bulb to allow for thermal expansion of a thermally conductive liquid.
2. Related Art
Traditionally, lighting has been generated using fluorescent and incandescent light bulbs. While both types of light bulbs have been reliably used, each suffers from certain drawbacks. For instance, incandescent bulbs tend to be inefficient, using only 2-3% of their power to produce light, while the remaining 97-98% of their power is lost as heat. Fluorescent bulbs, while more efficient than incandescent bulbs, do not produce the same warm light as that generated by incandescent bulbs. Additionally, there are health and environmental concerns regarding the mercury contained in fluorescent bulbs.
Thus, an alternative light source is desired. One such alternative is a bulb utilizing an LED. An LED comprises a semiconductor junction that emits light due to an electrical current flowing through the junction. Compared to a traditional incandescent bulb, an LED bulb is capable of producing more light using the same amount of power. Additionally, the operational life of an LED bulb is orders of magnitude longer than that of an incandescent bulb, for example, 10,000-100,000 hours as opposed to 1,000-2,000 hours.
While there are many advantages to using an LED bulb rather than an incandescent or fluorescent bulb, LEDs have a number of drawbacks that have prevented them from being as widely adopted as incandescent and fluorescent replacements. One drawback is that an LED, being a semiconductor, generally cannot be allowed to get hotter than approximately 120° C. As an example, A-type LED bulbs have been limited to very low power (i.e., less than approximately 8 W), producing insufficient illumination for incandescent or fluorescent replacements.
One potential solution to this problem is to use a large metallic heat sink attached to the LEDs and extending away from the bulb. However, this solution is undesirable because of the common perception that customers will not use a bulb that is shaped radically different from the traditionally shaped A-type form factor bulb. Additionally, the heat sink may make it difficult for the LED bulb to fit into pre-existing fixtures.
Another solution is to fill the bulb with a thermally conductive liquid to transfer heat from the LED to the shell of the bulb. The heat may then be transferred from the shell out into the air surrounding the bulb. As heat is transferred from the LED to the conductive liquid, the temperature of the liquid increases, resulting in an increase in the liquid volume due to thermal expansion. Some liquid-filled LED bulbs use a pocket of air or bubble in the bulb. As the temperature of the liquid increases, the volume of the liquid expands, and the pocket of air or bubble is compressed.
However, it is undesirable to have a pocket of air or bubble in the liquid-filled bulb. First, a pocket of air reduces the cooling efficiency of the bulb by creating an air barrier between the liquid and at least a portion of the outer shell housing. Second, the bubble may distort the light created by the LED, resulting in a non-uniform light distribution. The bubble may create a bright reflection or darkened area detracting from the visual appeal of the bulb. Third, an air bubble draws attention to the fact that the bulb is filled with a liquid, which may not be appealing to customers.